To add on to what you found and Virtox added, Ceramics is the only certified food safe material. This is because the glazing process is a certified food safe process. So if you us another material, it would be up to you to use a food safe process to make it work.

I learned a long time ago the wisest thing I can do is be on my own side, be an advocate for myself and others like me. -Maya Angelou
michael@shapeways.com Community Advocate

The minimum wall thickness for ceramics is 3 mm or more depending on the size:
Min Wall Supported:
If bounding box x+y+z is 120-200mm: 3mm
x+y+z is 200-300mm, min wall should be 4mm
x+y+z is 300-400mm, min wall should be 6mm

And if you want a hollow cavity in a model there needs to be a hole for the "support" material to get out:
Min Escape Hole:
10-15mm diameter

Ceramics is special in that it is priced per surface area, not per volume. (Suggests that
the glazing is an order of magnitude more expensive than the clay).
So adding holes can actually make your model more expensive in ceramics.